Realizing a Dream – The indigenous Cryogenic Engine

During the 90's, India seeking to launch INSATs weighing more than two tonnes, was scouting for cryogenic engines to power its GSLVs. Work on developing India's own cryogenic engine was started by ISRO shortly after the project to develop the GSLV was initiated in 1986. With an initial project cost of about Rs 235 crore, the work for the development of India's own cryogenic engine was jointly carried out by the Liquid Propulsion Systems Centre (LPSC) in Trivandrum, Material Development and Research Centre at Vikram Sarabhai Space Centre (VSSC). Though India has her own plans for developing an indigenous engine, the plan was to fast track development time by procuring technology from outside.

Cryogenic engines are essential to put heavier satellites into geo-synchronous transfer orbits (GTO) at an altitude of 36,000 km. Cryogenic propulsion enables a launch vehicle to put a payload two times heavier than that orbited by a vehicle without a cryogenic upper stage. It was essential that they be employed in GSLV rocket if it were to launch a 2000 kg class INSAT communciation Satellite to geo stationary orbits.

A cryogenic engine is powered by cryogenic propellants - liquid oxygen as oxidiser and liquid hydrogen as fuel. A bi-propellant combination of LH-LOX offers a higher specific impulse than the semi-cryo or fully earth-storable combinations. This implies that a fully cryogenic engine can deliver a higher payload mass for a given weight of on-board fuel. Since they are gases at room temperature, they require use of the cryogenics or techniques and systems at sub-zero temperatures to liquefy them. Liquefying oxygen and hydrogen, maintaining and handling these cryogenic fluids is an extremely demanding and tough task. At such low temperatures, metals become brittle. New welding techniques, new alloys and new types of lubricant are required. Liquid hydrogen and liquid oxygen had to be pumped into the engine in the right proportions.

Initially, General Dynamics (USA) and Arianespace were willing to sell the cryo engine and offered to transfer technology. But the cost was very prohibitive. Then the Russians approached India and a deal was stuck with Glavkosmos in 1991 for Rs.235 crores which included total cryogenic technology transfer and the supply of two KVD-1 engines.

But the U.S. played spoilsport, pressuring Russia not to sell the technology to India on the grounds that it violated MTCR agreements and that the missile-related technology and equipment transfers to non-member countries is restricted . The Pokhran-II nuclear tests in May 1998 further complicated the problem.

Russia backed out from transferring the cryogenic engine technology under American pressure. The 1991 deal had to be renegotiated subsequently in 1994 without technology transfer as per the original deal. Instead Russia agreed to supply ready built and complete cryogenic stages. The Russians also supplied the supporting equipment. ISRO built massive ground facilities to store liquid hydrogen and liquid oxygen.

The cryogenic engine supplied by Russia was tailor made for GSLV and ISRO’s requirements. Russia was prepared to sell India a cryogenic engine stage that developed a thrust of 10 tonnes as againt the current 7.5 tonnes. Though Russia supplied the cryogenic stage, ISRO insisted that it will develop its own electronics, guidance and control systems for the cryogenic stage. A cryogenic stage in a launch vehicle consists of the engine kept in a casing and the associated control, guidance and electronic systems. The thrust chamber is the powerhouse of the engine where combustion of fuel and oxidiser takes place. The burnt gases are ejected through a nozzle, converting the thermal energy of the combusted products into kinetic energy. The cryogenic engine thrust chambers need to be cooled to protect them from high temperatures. Materials of high thermal conductivity such as copper and its alloys are used for chamber construction. The tanks and pipelines are double-walled, insulated and vacuumed. The fuel and oxidiser itself is circlated around the nozzle surface to cool it.

While an entire GSLV flight lasts approximately for 1,050 seconds to inject the satellite into the orbit, the cryogenic engine alone operated for 700 seconds. That’s more than 66% of the entire flight duration. The cryogenic engine hurls the satellite at a velocity of 10 km a second into the orbit. While the earth storable liquid propellants could be loaded easily into the vehicle stages, the cryogenic propellants evaporated easily during storage. So in the GSLV, the cryogenic propellants are loaded just 3-4 hours prior to the launch. The final level is achieved in the last 10 minutes. This ensures that precise conditions needed at the lift-off for the quantity of propellants, their temperature and pressure are met.

In a PSLV, the core liquid motor is ignited first and the vehicle lifts off. Later, the solid strap-on motors are ignited. In the GSLV however, the 4 liquid strap-on motors are ignited first and their performance checked. After a gap of 4.6 seconds, the core solid stage is ignited. This gap is to confirm that all the 4 strap-on motors have developed the required thrust. So in both cases, if the liquid motor does not develop the required thrust, the entire flight is aborted and the liquid motors are shut down. The liquid stage is de-fuelled and defects analysed. One the issue is rectified, they can be re-fuelled and new countdown can be resumed. This is not possible with a solid fuel stage. This was demonstrated during GSLV flight on March 28, 2001 when it was aborted just 1 sec before lift-off.

During a GSLV launch, at T-10 minutes, automatic launch sequence (ALS) computer takes over the operations. At T-4.6 seconds, the 4 liquid strap-on liquid motors containing 42 tonnes of propellant are ignited and their performance checked. At T-0 sec, core first stage, powered by 138 tonnes of solid propellant is ignited. After lift-off, the first stage burnt for 105 seconds and the strap-ons for 148 seconds, taking the vehicle to an altitude of 70 km. The second stage, with 39 tonnes of liquid propellants, ignites at 1.6 seconds before the burnout of the last of the four strap-on stages. The second stage is fired for another 140 seconds, taking the vehicle to an altitude or 130 km, and its velocity to 5.4 km a second. When the vehicle reaches a height of 115 km, it would have cleared the dense atmosphere, The "Heat Shield" which protects the satellite from getting overheated splits down and jettisoned. At around t-290 secs or 292 seconds after lift-off, the third cryogenic stage is ignited. Cryogenic stage, which carries liquid oxygen and liquid hydrogen weighing 12 tonnes together, fires for 704 seconds. The satellite and the equipment bay reach an altitude of 206 km. Then the stage injects the geo-stationary satellite into the required orbit with a velocity of around 10.24 km a second.

Indian Cryogenic Engine

The indigenous cryogenic engine develops a thrust of 73 kilo Newtons (kN) in vacuum with a specific impulse of 454 seconds and provides a payload capability of 2200 Kg to Geosynchronous Transfer Orbit (GTO) for GSLV. The engine works on 'Staged Combustion Cycle' with an integrated turbopump running at around 42,000 rotations per minute (rpm). It is also equipped with two steering engines developing a thrust of 2 kN each to enable three-axis control of the launch vehicle during the mission. Closed loop control of both thrust and mixture ratio ensures optimum propellant utilization for the mission.

The Indian Cryogenic Stage
As of 2008, the development of the indigenous cryogenic engine has been completed. Full duration tests, with the engine burning for 1,000 seconds, have been done. The engine is integrated with its stage i:e electronics, guidance, control systems, fuel tanks, fuel supply lines etc. This entire stage has been qualified. ISRO had tested several cryogenic engines for a cumulative duration of 7,500 seconds. The engine now stands tall ready for its first flight in April 2010. A successful launch would make India totally self-reliant in all aspects of space launch vehicle technology

Gaining confidence from its monumental effort, ISRO is also preparing a new cryogenic engine from scratch starting from the drawing board. Codenamed C-25, this all new engine will have 25 tonnes of propellants developing a thrust of 20 tonnes. This will power the upper stage of GSLV-III

India will realize it dream in April 2010 with a successful launch of GSLV-D3. More than a decade old effort of developing a cryogenic engine will bear its fruit. All the best ISRO. Make us proud

Indian Space Research Organisation on Wednesday said there was no Russian involvement in the design and production of cryogenic engine that is developed by New Delhi indigenously and declared that it's a befitting reply to the technology denial regimes.

India is set to test the home-grown cryogenic stage and technology -- developed after 18 years of research -- in its rocket, GSLV, on April 15 from the Sriharikota spaceport.

Asked at a press conference here if Russians were involved in the development of cryogenic technology, ISRO Chairman K Radhakrishnan said India certainly learnt a lot working with Moscow and it was a "good learning experience".

But he asserted: "The (cryogenic) engine is designed by our own engineers, our own industry fabricated it, tested...". He added: "It's Indian. You should be proud of it".
ISRO officials recalled that the US exerted pressure on Russia not to provide cryogenic technology and India took a bold decision in 1992 to develop it indigenously.

Of the seven engines supplied by Russia earlier, ISRO has used five. Radhakrishnan said India developing this complex technology is a "befitting reply" to technology denial regimes.
"About Rs 335 crore is the amount used for the development (of indigenous cryogenic engine and stage)," Radhakrishnan said.

The Rs 175-crore GSLV-D3 would carry the Rs 150-crore, 2220 kg GSAT-4 experimental communications satellite in the proposed mission on April 15. The ISRO chairman said the PSLV mission, which would launch Cartosat-2B, an Algerian satellite, two Canadian nano-satellite, and Studsat developed by Indian students, is slated in the first half of May.

The indigenously developed cryogenic rocket, scheduled to be launched on Thursday, involves the highest level of technology and its success will make India one of the world leaders in rocketry, according to a top space scientist.

"It's actually going to be a major milestone, and it's one of the path-breaking development that we have done," former Chairman of Indian Space Research Organisation G Madhavan Nair who has been involved in the project said.

After one-and-half decades of research and development, India is now set to flight-test the home-made cryogenic stage and engine in the GSLV-D3 flight scheduled to be launched from the Sriharikota spaceport on April 15.

"Without anybody's assistance, India has really developed the cryogenic technology. We have set our goals and worked for it and we have achieved it. (It's) Not to show about our strength and things like that," told PTI.

"We hope that the flight will be alright".

Nair said development of cryogenic technology was a challenging job.

In his tenure as the Director of ISRO's Liquid Propulsion Systems Centre from 1995-99, India's efforts towards indigenous development of cryogenic technology took concrete shape and vital infrastructures were built and critical technologies were developed.

"This is the highest levels of technology in rocket," Nair said. "So, that way we are mastering that. I think we are becoming one of the world leaders in rocketry," he said.

The forthcoming launch of the Geosynchronous Satellite Launch Vehicle (GSLV) will be a watershed for the Indian Space Research Organisation, marking the culmination of the quest for cryogenic technology that dates back to over 25 years and has seen many twists and turns.

Cryogenic technology involves the use of rocket propellants at extremely low temperatures. The combination of liquid oxygen and liquid hydrogen offers the highest energy efficiency for rocket engines that need to produce large amounts of thrust. But oxygen remains a liquid only at temperatures below minus 1830 Celsius and hydrogen at below minus 2530 Celsius. Building a rocket stage with an engine that runs on such propellants means overcoming engineering challenges.

The United States was the first country to develop cryogenic rocket engines. The Centaur upper stage, with RL-10 engines, registered its first successful flight in 1963 and is still used on the Atlas V rocket. America's early mastery of the technology paved the way for the J-2 engine, which powered the upper stages of the immensely powerful Saturn V rocket that sent humans to the Moon.

Other spacefaring nations followed. The Japanese LE-5 engine flew in 1977, the French HM-7 in 1979 and the Chinese YF-73 in 1984. The Soviet Union, first country to put a satellite and later a human in space, successfully launched a rocket with a cryogenic engine only in 1987.

ISRO recognised the importance of cryogenic technology fairly early. A rocket stage based on a cryogenic engine offered the simplest way of transforming the Polar Satellite Launch Vehicle (PSLV), intended to carry one-tonne earth-viewing satellites, into the far more powerful GSLV that could put communications satellites into the orbit.

In December 1982, six months after the PSLV project was cleared, a Cryogenic Study Team was set up. A year later, it submitted a report recommending the development of a cryogenic engine that could generate about 10 tonnes of thrust. The 15-volume report went into every aspect of developing the engine and rocket stage indigenously.

Then, strangely, ISRO went through a long period of indecision, dithering on whether to buy the technology or develop it on its own. Acquiring the technology from abroad would greatly reduce the time that would otherwise be needed, it argued.

But the U.S., Japan and France would either not provide the technology or do so only at an exorbitant price. Finally in January 1991, a deal was signed with the Soviet company Glavkosmos to buy two cryogenic flight stages as well as the technology to make them in India.

The 11D56 cryogenic engine had been developed for one of the upper stages of the mammoth N1 rocket, the Soviet equivalent of Saturn V. But after four successive launch failures, the N1 project was scrapped and its engines were mothballed. Under the Indo-Soviet deal, ISRO would get a stage built around the 11D56 cryogenic engine that could produce 7.5 tonnes of thrust. The stage would carry 12 tonnes of propellant.

But the deal violated the Missile Technology Control Regime, which was intended to prevent the spread of missile-related technology, and fell foul of the U.S. laws meant to enforce its provisions. Despite warnings from within the organisation, ISRO opted to go ahead with the import. In May 1992, the U.S. imposed sanctions on ISRO and Glavkosmos. A year later, Russia, which inherited the contract after the break-up of the Soviet Union, backed out of the deal.

ISRO then had no option but to develop the technology on its own. The Cryogenic Upper Stage project was launched in April 1994. Its aim was to develop a cryogenic engine and stage closely modelled on the Russian design.

At the time, ISRO gave the impression that much of the technology had already been acquired and further development would be quick. A GSLV with an indigenous cryogenic engine would be ready to fly in about four years, Chairman U.R. Rao told The Hindu in July 1993. The space agency's engineers were privately saying then that a flightworthy cryogenic stage was 10 years away. Instead, it has taken 16 years.

The Russian design involves a complicated â€˜staged combustion cycle' to increase the engine efficiency. Hydrogen is partially burnt with a little oxygen in a gas generator. The hot gases drive a turbopump and are then injected at high pressure into the thrust chamber where the rest of oxygen is introduced and full combustion takes place. Before going to the gas generator, the incredibly chilly liquid hydrogen is used to cool the thrust chamber where temperatures rise to over 3,0000 Celsius when the engine is fired.

Reproducing the Russian design meant ISRO engineers also learning to deal with new materials and manufacturing methods. A process, known as vacuum brazing needed to make the engine's thrust chamber, for instance, took considerable time to master. Then there was the challenge posed by the powerful turbopump that rotates at a tremendous speed in order to send up to 18 kg of propellants every second into the thrust chamber. It must do so in the face of a sharp temperature gradient, with hot gases at over 5000 Celsius driving the turbine, which then spins the pumps for freezing-cold propellants.

Steps were also taken so that materials required for the engine and stage could be made within the country.

The Indian cryogenic engine is produced by Godrej and the Hyderabad-based MTAR Technologies working together as a consortium. Instead of ISRO first mastering the technology and transferring it to industry, the two companies were involved from the start and even the early prototypes were built by them. Failure on their part was not an option and the space agency had to make sure that these companies succeeded.

Finally, in February 2000, the first indigenous cryogenic engine began to be test-fired on the ground. According to one source, things went wrong in one test and an engine ended up badly damaged. However, by December 2003, three engines had been ground-tested for a cumulative duration of over an hour and half. One of those engines was fired continuously for more than 16 minutes, four minutes longer than it would operate in actual flight. More tests with the engine integrated into the full stage followed. The cryogenic engine that will fly in the forthcoming GSLV launch was tested on the ground for a little over three minutes in December 2008.

Meanwhile, the Russians had supplied ISRO with seven ready-to-fly stages. But their 11D56 cryogenic engine had not flown before and the Indians faced some unpleasant surprises.

The first was that the Russian-supplied stages turned out to be heavier than expected. In order to carry the extra load, it is learnt, the Russians increased the maximum thrust that the 11D56 engine was capable of â€” from 7.5 tonnes to a little over eight tonnes. The engine operates at the higher thrust for only part of the duration of its flight. The Indian engine too had to be tested and made to work at the higher thrust level. Moreover, the Indian stage is lighter than the Russian one.

When the GSLV was first launched in April 2001, the Russian cryogenic engine was found to be less efficient than predicted, based on a measure that rocket engineers call specific impulse. The increase in stage weight and decrease in efficiency together reduced the rocket's payload capacity significantly.

Where the GSLV with the cryogenic stage was intended to put 2.5 tonnes into the orbit, the rocket carried a satellite weighing just 1.5 tonnes in its first flight. With further optimisation of the Russian cryogenic stage and other parts of the rocket, the GSLV could successfully launch the 2,140-kg Insat-4CR in its fifth launch in 2007.

Sources told this correspondent that the last two stages supplied by the Russians carry an engine with a maximum thrust of over nine tonnes and are capable of accommodating an additional three tonnes of propellant. The GSLV with this stage would be capable of delivering a payload of 2.5 tonnes into the orbit. With further ground testing, the Indian engine too would be upgraded to a similar thrust level.

But the immediate challenge for ISRO and its engineers is to demonstrate in the GSLV launch that they have indeed mastered the intricacies of cryogenic technology.